Two-stage transmission for electrically driven vehicle

Abstract

The present invention relates to a two-stage transmission for an electrically driven vehicle including a dog clutch and a friction clutch, and an object of the present invention is to prevent a torque drop when shifting gears. The two-stage transmission for the electrically driven vehicle includes a planetary gear mechanism (12), a dog clutch (28), a friction clutch (30), an armature (26) to switch between the dog clutch (28) and the friction clutch (30), and an electromagnetic coil (31) to drive the armature (26). In the dog clutch (28) and the friction clutch (30), the coupling relationship among the rotational elements of the planetary gear mechanism (12) is set such that the dog clutch (28) is fastened and the friction clutch (30) is not fastened in speed reduction (the first speed), and the dog clutch (28) is not fastened and the friction clutch (30) is fastened in speed increase (the second speed). To prevent the torque drop when shifting the gears, a ratchet-type one-way clutch (50) is disposed such that a rotational phase position of the ratchet-type one-way clutch (50) is coincident with that of the dog clutch (28). When shifting from the second speed to the first speed, since the rotational phase of the dog clutch (28) is adjusted by the ratchet-type one-way clutch (50), the shifting is instantaneously completed without waiting operation for the phase adjustment, resulting in preventing a transmission shock.

The invention claimed is: 
     
       1. A two-stage transmission that is disposed along an output axis of an electric motor in a vehicle using said electric motor for wheel driving, comprising:
 a planetary gear mechanism which comprises three rotational elements including a carrier pivotally supporting plural pinions and plural gears which have a different tooth number and engage with said pinions, and uses a first speed mode in which a first rotational element selected from said three rotational elements is fixed to a housing side and power transmission is performed by using a gear ratio whose value is different from 1.0 and which is obtained between a second rotational element and a third rotational element, and a second speed mode in which said power transmission is performed by using said gear ratio whose value is 1.0 and which is obtained by fixing said first rotational element to a housing side and inputting from and outputting to one of said second rotational element and said third rotational element, or by not fixing said first rotational element to said housing side and integrally rotating one of said second rotational element and said third rotational element with said first rotational element; 
 a dog clutch which couples with said rotational elements of said planetary gear mechanism to select a relatively low gear ratio side speed mode between said first speed mode and said second speed mode; 
 a friction clutch which couples with said rotational elements of said planetary gear mechanism to select a relatively high gear ratio side speed mode between said first speed mode and said second speed mode; and 
 a ratchet-type one-way clutch to prevent a torque drop when shifting between said first speed mode and said second speed mode, 
 wherein engagement portions of said dog clutch and a ratchet engagement portions of said ratchet-type one-way clutch are arranged at the same rotational phase position. 
 
     
     
       2. The two-stage transmission for the electrically driven vehicle according to  claim 1 ,
 wherein said first rotational element selected from said three rotational elements of said planetary gear mechanism is permanently fixed to said housing side, 
 wherein said first speed mode in which a reduction speed side gear ratio whose value is larger than 1.0 is obtained between said second rotational element and said third rotational element by using said dog clutch, serves as said relatively low gear ratio side speed mode, 
 wherein said second speed mode in which a gear ratio whose value is 1.0 is obtained by inputting from and outputting to one of said second rotational element and said third rotational element of said planetary gear mechanism by using said friction clutch, serves as said relatively high gear ratio side speed mode, and 
 wherein, when shifting between said first speed mode and said second speed mode, said one-way clutch prevents said torque drop by locking said second rotational element or said third rotational element to an input axis side such that transmitting rotation is surely performed. 
 
     
     
       3. The two-stage transmission for the electrically driven vehicle according to  claim 1 ,
 wherein said first rotational element selected from said three rotational elements of said planetary gear mechanism is selectively fixed to said housing side, 
 wherein said first speed mode in which said first rotational element is fixed to said housing side and a gear ratio whose value is larger than 1.0 and which becomes a reduction speed side gear ratio is obtained between said second rotational element and said third rotational element by using said dog clutch, serves as said relatively low gear ratio side speed mode, 
 wherein said second speed mode in which said first rotational element is released from said fixing to said housing side and a gear ratio whose value is 1.0 is obtained by integrally rotating one of said second rotational element and said third rotational element with said first rotational element by using said friction clutch, serves as said relatively high gear ratio side speed mode, and 
 wherein said one-way clutch prevents said torque drop by locking said first rotational element to said housing side such that power transmission from an input side to an output side is surely performed.